This invention relates to tufting machines and more particularly to a method and apparatus for tufting cut pile of different levels in the same row of stitching.
Numerous attempts have been made for selectively forming different pile heights by each needle of a cut pile tufting machine. For example, in U.S. Pat. No. 3,138,126 a hook having first and second vertically spaced blades in which the bill of the lower blade has a spring clip is illustrated. Yarn tension produced by a yarn feed control mechanism selectively moves the clip to open and close passage of a loop onto the lower blade. When the spring is pulled away from the lower bill the loop is shed and seized by the upper bill to produce a low cut pile tuft. If sufficient yarn is fed to the needle the spring clip remains in engagement with the lower bill and prevents sheding to form a high cut pile tuft. Back-drawing of the yarn by the feed mechanism effects the high tension to release the clip. In U.S. Pat. No. 3,075,482 a similar arrangement is disclosed for producing three levels of pile, a high and medium cut pile and a low loop pile.
In U.S. Pat. Nos. 3,820,482 and 4,029,029 the hooks have spaced upper and lower blades, the bills of the upper blades having a lower surface below the bills of the lower blades and shaped to allow a loop to travel toward the lower bill. Both of these patents utilize a knife for each blade and a yarn feed control mechanism for controlling whether the loops are received onto the lower bill or pulled through the space between the bills and caught by the upper blade. Consequently, in all of the known prior art proposals to produce a high and low cut pile in the same row of stitching, a yarn feed control system in which the amount of yarn being fed for each stitch and thus the tension on the yarn provides the control force which effects the height of the pile produced.